The present invention relates to a method of fabricating a micro-electro-mechanical (MEM) device having a switching mechanism that is based on induced a magnetic force and a method of fabricating such a device.
MEM switches are superior to conventional transistor devices in view of their low insertion loss and excellent on/off electrical characteristics. Switches of this kind are finding their way into an increasing number of applications, particularly in the high frequency arena.
By way of example, U.S. Pat. No. 5,943,223 to Pond described a MEM switch that reduces the power loss in energy conversion equipment, wherein MEM devices switch AC to AC converters, AC to DC converters, DC to AC converters, matrix converters, motor controllers, resonant motor controllers and other similar devices.
Known in the art are MEM switches that are designed using a variety of configurations which are well adapted to perform optimally in many different applications.
For instance, U.S. Pat. No. 6,667,245 to Chow et al. describes a cantilever type MEM switch illustrated in FIG. 18, consisting of: 1) upper plate 71; (2) lower plate 74; (3) lower contact 19; (4) upper contact 29; (5) interconnect plug 27 and (6) cantilever 72. When current flows between upper plate 71 and lower plate 74, an electrostatic force is established, attracting upper plate 71 and bending cantilever 72 downwards toward 14, making contact between two contact points 19 and 29.
Another configuration uses a torsion beam, as described in U.S. Pat. No. 6,701,779 B2 to Volant et al., of common assignee. The perpendicular torsion micro-electro-mechanical switch, illustrated in FIGS. 19A and 19B, respectively show a side view and a top-down view thereof. It depicts a switch consisting of five key elements; 1) movable contact 20; (2) stationary contact 30; (3) stationary first control electrode 40; (4) flexible second control electrodes 50 and 50A; and (5) torsion beam 60. Electrodes 40 and 50 are attracted to each other when a DC voltage is applied therebetween, causing torsion beam 60 to bend. Since the movable contact 20 is attached to torsion beam 60, it will, likewise, move downward, making contact to the stationary contact 30.
In yet another configuration, a micro-electromechanical inductive coupling force switch is described in U.S. Pat. No. 6,831,542 B2, of common assignee, and illustratively shown in FIG. 20. The MEM device consists of at least five elements: 1) movable coil assembly 10; (2) moveable inductor coils 20 and 30 rotating around pivot pin 75; (3) stationary coils 40 and 50; (4) comb drives 8 and 9; and (5) conductors coupled to the moveable inductor coils 20 and 30. The coupling force of the coils (20 and 40, 30 and 50 can either be negligible or very strong depending on the position of the assembly which is adjusted by comb drives 8 and 9). In its fully coupled condition, current flowing into coil 40 induces a current into inductor coil 20. Since inductor coils 20 and 30 are interconnected, the same current will flow to 30, which in turn induces a current in stationary coil 50.
A further configuration, described in U.S. Pat. No. 6,452,124 B1 to York et al., shows a capacitive membrane MEM device illustrated in FIG. 21. Therein, a MEM switch is shown consisting of four basic elements: 1) upper metal electrode 102; (2) lower metal electrode 104; (3) insulator membrane 108; and (4) metal cap 110. When a DC voltage potential is applied between 102 and 104, electrode 102 bends downward and makes contact with metal cap 110, closing the switch.
Magnetic coupling providing an angular displacement for actuating micro-mirrors is described in U.S. Pat. No. 6,577,431 B2 to Pan et al. This assembly is illustrated in FIGS. 22A and 22B, respectively showing a perspective view and a side view thereof. It consists of three basic elements: 1) reflection mirror 44; (2) orientation mirror 43; and (3) permalloy material 441 and 431. When current passes through actuator 46, the two permalloy elements induce a magnetic field, creating a repulsing force and bending the mirrors away from the substrate. Both the reflection mirror 44 and the orientation mirror 43 are supported by way of 42a onto a glass or silicon substrate 41.
Other related patents include:
U.S. Pat. No. 6,166,478 to Yi et al. which describes a micro-electro-mechanical system that uses magnetic actuation by way of at least two hinged flaps, each having a different amount of permalloy or other magnetic material.
U.S. Pat. No. 5,945,898 to Judy et al. describes a magnetic micro-actuator having a cantilever element supported by at least one mechanical attachment that makes it possible to change the orientation of the element and of at least one layer of magnetically active material placed on one or more regions of the cantilever.
U.S. Pat. No. 6,542,653B2 to Wu et al. describes a micro-switch assembly involving a plurality of latching mechanisms.
Still missing and needed in the industry is a low cost, highly reliable MEM switch that is compatible with CMOS fabrication techniques but which dispenses with the need for large open cavities which are difficult to cover, and even harder to properly planarize. There is a further need in the industry that this MEM switch be hinge free, i.e., devoid of mechanical moving parts in order to achieve durable and reliable switching.